The impact of reduced frequency of cage changes on the health of mice housed in ventilated cages. Laboratory Animals 35: 58–73

Summary Our purpose in this investigation was to determ ine if we could reduce cage changing frequency without adversely affec ting the health of mice. We housed mice at three different cage changing frequencies: 7, 14, and 21 days, each at three different cage ventilat ion rates: 30, 60 and 100 air changes per hour (ACH), for a total of nine experimental conditions. For each condition, we evaluated the health of 12 breeding pairs and 12 breeding trios of C57BL = 6J mice for 7 months. Health was assessed by breeding performance, weanling weight and growth, plasma corticosterone levels, immune function, and histological examinat ion of selected organs. Over a period of 4 months, we monitored the cage microenvironment for ammonia and carbon dioxide concentrations, relative humidity, and temperature one day prior to changing the cage. T he relati ve humidity, carbon dioxide concentrations, and temperature of the cages at all conditions were within acceptable levels. Ammonia concentrations remained below 25 ppm (parts per million) in most cages, but, even at higher concentrations, did not adversely affec t the health of mice. Frequency of cage changing had only one signi®cant effect; pup mortal ity with pair mat ings was greater at the cage changing frequency of 7 days compared with 14 or 21 days. In additi on, pup mortality with pair matings was higher at 30 ACH compared with other ventilat ion rates. In conclusion, under the conditions of this study, cage changes once every 14 days and ventilation rates of 60 ACH provide optim um conditions for anim al health and practical husbandry